Submarine signaling cable



Jan. 29,. 1929. 1,700,476

J. J. GILBERT SUBMARI NE S I GNALNG CABLE Original Filed Feb. 27, 1926lliiis invention relates to sulnnziiiiie signeh ing.

in olii ect of the invention is to inciezise the timisinissionetliciency of submarine signalcables.

i, is also ein object of the invention to i'e duce the increment ofeffective ieSiStnnce o'j e s. dnnnriiic signaling celole due to thepresoit tei'ede tape employed to protect insnletion et the cable 'freinravages et, teiedo is also en object oi 'the invention to pio vide nnei'licient ifeturn path oi sigi'ieiliiip; cui'- ients of comparativelyhigh frequencies in a eulnnei'ine cable.

eeen found that when n celile is pio y t vicedivith both teredo tape:incl continuous lending, the .leading hei/inn" the oifin of one eiinoie helical inenieeis high permeability ticncv is occasione/(tbvreason of the feet V; n coneiueieble increment in the effective thecable can' arise :troni the fes in the terede tape, theselosses tesult-"cents, which foi* convenience in y currents, flowing in the tape e ofelec'tieinotive 'foi'ces set up iij/ the varying; magnetic fiul endingnieteiinl by signaling` ne flowing in the cable. in accordance thisinvention, this increment et effeci'esictnnce is reduced by employing; n

oi .like protective layer having high i'cf: i i `vitvl lwi, inaccordance 'with tine 1nvcul'ion, this -i cicincnt of effectiveresistance l luv o; the tape, as for exemple, liv incfiensine` wid `i,and insulating' adjacent tui-ne of the tzije l'i'e i cncli othci.lllheie the nuling involi'ci; fiequencies Suiicientlv high to ien deiYv:tsillic return path foi the sign i :Ulviseolc, in accordance with 'theinventioA there is in vided such n' return nath comprisf helicalconductors having' high conducai nv ind iizivine n` large Ditch orlength of putin to* l eiv'n'iegnetizing forces, n innteiinl loss el"'eiluced by increasing the pitch o1' length of i' .une 2, 1928.

lav. 1in accordance with the invention 'these return condnctois may lieWithin the helix of the steel ninioi' 'vites for the celole, Wherelovthese etnici' wines will retain the return conductors on the cable andthus enable their pitch to lie inzide greater than would ethel Wise liepincticnlile, This long ley tenes to- Wei'd reduction et' the resistanceof the return any ,given annount ot' materiel in that pn n. oiVA tends;to enable reduction in the Weight oit the material in the return path,'for any given iesistunce of the path. n the ense of cable loadedmentioned above, this long` ley also tends te reduce loseee due to edd;Ycurrents in the ietuin path, these eddy currents insulting ionielectionietive forces set up in the material of the return path liv thevary ng n'iegnetic flux created in the loading; materiel ley thesignaling current.

@thee objects und ndvcntnges of the in vention Will lie :apparent 'freinthe following tion et' the cable o1' 1 e n dimvn to smaller l tiie cablecomprises n centi-eil conn loading' Wire oitnpe i surrounding; theconductor 5, lever of nutte perchaoi like insulation preferably nvi n`Wall tliiciniess oi P oni one to seveiel millimeters ne conducto? 5 andloading infil i the inlielicei Steel urine? jute and suii'eundine y c1ne coie li constituted luy Sulnftion El, vviief; cnil? s i3 niej; lieindividunlfiv c tape 19 and 'e compound.

npose ci niotec t f educing eddy currents es es xviii lieneintedeutheifennittei,

x Thev construction and advantages-of such -a -loaded cable conductorare described in'U., S.

patents to E. Buckley 1,586,874, June 1, 192e, e. W. itimen 1,585,884,June 1, 192e,

and O. E. `Buckley 1,%8'6,863, March 18, 192i.- The teredo tape f1", forprotecting the inf sulation 9 from/the attacks of the' teredov worm,`isa'he'lical wrapping surrounding a portion r,of/'the core that lies inneighborhoods Wherefthe teredo Worm is fou-nd. The length of/the corethat is supplied'with'teredo tape consists of thelportion of the cablethat lies in Water of a depth `less than about 10() fathoms. It is foundthat the teredo Worin does not ordinarily operate in depths greater thanthis. The teredotape is Wound on the 'core with suicient'overlap of theadjacent turns to insure against gaps in the metallic layer' lness-aluminum) formed by the tape. For reasons explained hereinafter,this tape ispreferably of material lhaving high resistivity, 4forexample, nichrome, Driver-Harris 193 alloy (nickeliron-chiomium), orTherlo (copper-manga- These alloys have resis tivity of 5 to 10 timesthat of brass, and also resist corrosion, so that they are suitable forAuse, in'sea-water. The teredo tape maybe of the ,order of .004 thick,and, for reasons explained hereinaftenits pitch or length of lay ispreferably.,substantially as great as it can be made without undue-riskof injury to the insulating material of the core. In general the Widthof the teredo tape may be three times the diameter of the core, so thatfor a core about 1/2 inch in diameter, the Width of l'the tape ispreferably about 1-1/2 inches.

a tape or Wire of magnetic material Wound helically on the conductor asdescribed above, the lines of magnetic induction produced by current inthe conductor tend to follow the helical path afforded bythe tape orwire, this tendency being' greater the higher the permeability of theloading material. 'lhat is, the lines of magnetic induction are notsingle loops around the conductor, but have the forni of a helix whichtakes a large number of turns around the conductor in one turn of theloadingtape before crossing an air gap to an adjacent turn ofthe loadingtape, the pitch of the helix of the lines of induction being slightlyless than the pitch of the tape, so that a line of induction follows thetape for, say, twenty turns around the conductor,

.then reaches thev rear edge of the tape and jumps backward across thesmall air ,gap to the adjacent turn and continues folowing the tape inthe original direction and 7o sense for another twenty turns, then againof the cableto the other and if the cable carried a Steady, directcurrent and Awere not subject to theeffect ofthe eaitths iield, thenlines of induction lWould-be continuous from one .end of the cabletothe other.) There exists, therefore, in the -loading'material acomponent of the magnetic induction parallel to the axis of theconductor, which may be termed the longitudinalor axial component /ofthe induction, this component `being approximately proportional vto thepermeability and to thev thickness of the loading material. It is alsodependent upon .the angle of lay of the loading tape or-Wire.. All otherconditions being the saine, the component of magnetic induction parallelto the axis of the conductor Will be greater theV greater the Widthconductor, which is proportional tol the time rate ofchange of the axialor longitudiv nal component of magnetic induction. This electromotiveforce causes a current to flow in the tape, and the energylossesresulting from this current ductor. In other Words, the losses in the.teredo tape give rise to an increment in the effective resistance ofthe cable conductor.

" This resistance increment can bel shown to iiovv arel taken vfrom theenergy of the signaling current in the conv los be proportional to thesquare of the frequency of the sinusoidal current, and to vary inverselyWith the thickness and resistivity of the teredo'itape, and to fall ofiIrapidly as the pitch or lay of the teredo tape is increased,

provided that .its adjacent turns are insulated.v

It has been found from measurements of actual Wire and tape loadedconductors for submarine cables that at a frequency 0f 60 cycles persecond, the increase ineffective resistance due to ordinary brassteredotape may amount to .1 ohm per mile. In the case ofa fairly heavytelegraph cable, the effect of this resistance incren'ient is toincrease the attenuation .constantofl the taped sections by as unich as3%. For cables of lighter weight than this, the effect 0n the attenua*tion constant will be less, since the resistance of the centralconductor is higher. The effect is not very serious in the case of along telegraph cable, since the frequency of signal-l ing is low andordinarily the taped portion of the cable is comparatively only a smallLAL fraction of the total cable length. For a telea large fraction ofits length, theeffect is more serious. -In either case'the magnitude ofthe resistance increment due to the electromotive-forces induced in theteredo tape, can be reduced by using in place of the customary brasstape, as described above.`suit able materiall such as nichrome,Driver-Harris 193 alloy, or Therlo. As noted above, these alloys haveresistivity of 5 to 10 times that of brass, and the currents dueto theelectromotive forces set up in the teredo tape are proportionately less,as are also the` corresponding values of resistance ,increment in thecable conductor.

It is also of advantageto increase the lay of the teredo tape, byincreasing its width to, for instance, a value of the order of threetimes the diameter of thecore, and to insulate adjacent turns of thetape, especially where they overlap. This insulation` she vn at 12, Fig.3, may be effected by providingl the teredo tape with an insulatingcover of oxide, for example, or by applying,T to it an insulatingcompound at the time it is being served on the core. In thisway theresistance aiforded by the tape to the inducing'electromotive force isincreased, since the current is caused to flow in the direction of thetape rather than in the shorter direction in a plane at right angles tothe central conductor, which is the direction of the inducingelectromotive force. Even where brass tape is used, this is ofadvantage,

Although it has already been found of advantage, so far as transmissionof high frevquencies through a submarine cable is concerned, to furnishthe cable with a return conductor consisting of a copper sheath made oftape wound helically around the core, nevertheless, asvpointed out in mycopending application, Serial No. 680,170, filed December 1:2, 1923,entitled Submarine cables, it is found that this method is not practicalfor low' frequencies, for instance, frequencies of a range from zero to100 cycles per second. For, unless the resistance of the sheath alone iscomparable in magnitude with the sca-water resistance without thecoppersheath the return resistance wiltbe increased by the addition of thecopper sheatli/i'lhis is because the screening action of the sheath issuch as to confine to the sheath the greater part of the return current.'ln the range of frequencies from zero to 100 cycles per second withcables such as are now in use for transoceanic operation,

this condition would-require such a large amount of copper in the sheaththat the cost and weight of the cable would be increased beyondpractical limits. therefore proposes to decrease the sea-returnresistance for the signaling frequency range just mentioned and, in someinstances, much That applicationhigher frequencies,- by employing, inplace of the usualsteel armor wires for the cable, varmor wires of highresistivity material, for example, nickel steel, chromium steel, orKrupp steel.

lVhere the cable of Fig. 1 is to be employed for signaling frequenciesof the range just mentioned, its ,armor wires may, accordingly,

vbe of such high resistivity material. 7Where the cable is loaded as inthe case of the cable of Fig. 1, the high resistivity of the armor wireshas the additional advantage of reducing eddy current losses produced inthe armor wiresby the lux in the loading materiaLin the same manner inwhich that flux produces eddy current losses in the teredo tape.

Fig. 2 shows a cable similar to that of Fig. l butha'vino` a metallicreturn path for signalingr currents, the return path comjirisingmaferial. of high electrical conductivity compared to that of steel.Identical elements 1n the two figures are indicated by the samere'lerence characters. The metallirI return path' is constituted by alayer of helical copper wires 31 or strips embedded in the jute 15 andlyingV between the steel armor wires 13 and the teredo tape 11 andsurrounding the core 1T and tape 11. This return path is especiallyuseful where the cable is to be employed for transmitting' fairly highfrequencies, for instance, frequencies of the voice range or somewhathigher. The-wire conductors 81 may be individually wrapped with tape 19as in the case of the armor wires 13. rlhe eddy current losses producedin the return conductors 31 by the flux in the loading` material in themanner in which such losses are produced in the tcredo tape b v thatflux, 'will not be unduly large because the conductors 31 are insulatedfrom each other and are given a long lay, for example, a pitch of theorder of three feet, so thatthe currents produced in these conductors bythe axial component of the magnetic flux in the loading material areforced to traverse a long path'. The length of this path is also duepartly to the fact that the conductors 31 are spaced a considerabledistance from the 1 teredo tape'll, thus making the diameter of thehelix of wires 31 large, and also increasing the maximum permissiblelength of lay of the wires 31. As shown in Fig. 3, the pitch of theconductors 3l is ,greater than that of the steel armor wires 13. lt ispossible to give the conductors 31 this greater pitch even where thepitch of the armor wires 13 is substantially the maximum valuepermissible, since the wires 81 are prevented from fallingr ott thecable by the wires 13. The long pitch of conductors 3l also has theadvantage that it increases the eihciency of the copper return path asa'longitudinal conductor. On this account the conductors 3l may containapproximately 20% less copper than would be necessary'` for a givenresistance of return conductor, if the return conductor were in the formof a. helical tapelaid onthe core.` With such a tape it is necessarytouse a--comparatively short lay in order to avoid injury to theinsulating material of the core. l i

Where desired, for instance. Where the cable 1 is to transmitfrequenciesso high that loading is impracticable or inadvisable, theloading material may be omitted from the cable of Fig. 2,.the spacingofthe return conductors from the central conductor being made suficienttov give the cable the desiied inductance'. .i It is pointed out in mycopending applicati'on, Serial No. 585,619,A filed September v1, 1922,entitled Submarine signalingcables, l5' i that-an' unloaded cable witha. concentric return conductor of high 'conductivity so spaced from thecentral conductor can have comparatively high 'efliciency forfrequencies at which loading would be inadvisable on-account of thelarge eddy current losses which would occur in the loading material.A

Similarly, ir desired, the loading 'material may be omitted from thecable of Fig. l,

Yvvheretlni frequencies to be transmitted by the cable are high, andsome or all of the armor with copper to serve as a return cir-cuit forthe cable can Well serve to transmit high freloading tape small, since,as noted above, they qiiencies. By making the pitch of the armor Wiresas great as is practicable, the efficiency 35 ofthe copper` pathas alongitudinal return conductor may be made large.

In another aspect the present invention..

covers the use of a teredo layer having high permeability, as Well as'-one or more of the characteristics described above as desirable forteredor protection. In such cases the layer \vill be constitutedof'material being suiicieiitly permeable to act as additional inductiveloading Which becomes-more effective as its spacing from the highconductivity metallic return is decreased.

Although it is lof advantage from the point of vie-iv of eddy jcurrentlosses to have the width and the pitch of the teredo tape large, it is'of advantage' from the same point ofd view to have the Width andVthepitch'oIfIthe component of magneticinduction parallelto theaxis ofthe central conductor will be greater the greater the Width' and thepitch'.

of the loading tape or wire, if other condi- .tions remain unchanged.The pitch of the teredo tape is preferably considerably greater thanthat of the loading tape or Wire.

Although the high resistivity metallic layei for affording protectionagainst the teredo has beenspecifically shown and described as ayhelical tape, it should beunderstood .that such disclosure isnotintended as precluding a broader view of the invention.

lVhat is claimed is: 'l

1. A lcontinuously loaded submarine `sig naling cable core comprising anelectrical conductor having loadingmaterial applied thereto, the loadingmaterial being surrounded by insulation, a helical metallic tape on saidcore, said tape having its adjacent turns overlapping, and insulationbetiveen the over-- lapping portions.

2. The combination vvith a continuously loaded submarine signaling cablecore comi prising-an electrical conductor surroundedv by helicalloading. aid .by a layerof insulation having a Wall thickness of atleast a millimeter,` of a 'helical metallic tape. on said core, saidtapehaving a thickness ofthe order of severalv thousandths of an finch. and`having resistivity at least twice that of brass. n

.f 3. A continuously loaded submarine signaling cable core, and ahelical metallic tape thereon having a. pitch substantially. greaterthan twice the diameter of vsaid core and having its adjacent-turnsoverlapping and insulated fiom each other. 1

4. A continuously loaded submarine cable c ore comprising an electrical-conductor surrounded by insulation and a helicalinetallic tape on saidcore, said tapefhaving'resistivity.

at least several times that` of brass, and having its adjacent turnsoverlapping and insulated from each other.

' 5, A continuously loaded submarine cable comprising aconductor,loading material, in-

sulation around said conductor and loading material, a metallic layeroutside said insula` tionA serving as protection'against the teredo,

said' loading material .being so associated with said conductor that acomponent of iiux is set up through the coil formed bysaid metalliclayer in the direction bf the length ofthe cable bythe signalingcurrents in said conductor, the resistivity of said `protective materialbeing high compared with that of iron.

6. A continuously Iload-ed subn'iarinesignaling cable Jcore comprisingan electrical conductor surrounded by a layer of loadingmaterial, alayer of insulation around tsaid loading material and a strip of metalof. high resistivity compared with brass around said Ainsulationivithncoi'itiguous edges' thereof oveilappingand insulated from eachother.

7. A submarine signaling cable, comprisinga central conductorcontinuously loaded with a helicall loading,nienibeifhaving high'permeability at low inagnetizing forces, asubstantiallyconcentric.return conductor for said central conductoi,\and electrical insulallO tion between said conductorsrsaid returncoiiduct-or having high' electrical YVconductivity compared to that ofsteel, and said return conj ductor comprising helical elements having apitch of the orderof at least a foot.

`8. 'A submarine signaling cable comprising a central conductorcontinuously` loaded with a helical loading memberhavinghighpermeabillty at loW magnetizing forces, a substantiallyconcentric returnl conductor torl at least one foot.l

9. A submarine cable comprising a central conductor, electricalinsulation surrounding said central conductor, a layer of helical Wiressurrounding said insulation, said Wires having conductivity high invcomparison to that of steel, and helical metallic armor memberssurrounding said helix of Wires, said ffarmor members.

Wires having a pitch greater thanthat of said 1.0. A continuously loadedcable comprising a central conductor, a helical element of highpermeability and high resistivity forining a layer thereabout,insulation surrounding said layer, and a layer ofy helically laid ytapeoutside said insulation having high resistivity compared With brass andhaving a greater pitch than said rst mentioned helical element. 1

l1. A submarine signaling cable comprising a loaded conductor,insulation thereabout, i

teredo tape external to the insulation, a return path externalto theteredo-tape, said path comprising a plurality of Wires of metal highlyconductive as compared to iron, separated from each other and from theteredo tape by material of Conducting properties very poor as comparedto iron.

12. A submarine signaling cable comprising a continuously loaded centralconductor, insulation surrounding said conductor, teredo tape externalto said insulation, a return path external to said teredo tape, saidpath comprising a plurality of Wires of metal highly conductive ascompared to iron, separated from each other and from the teredo tape bymaterial of conducting properties very poor as compared to iron, armorWires surrounding said return path and poor conducting material, theWires of said return path having a pitch greater than that of said armorWires.

13. A signaling cable comprising a signaling conductor, a return circuitpath spaced from said signaling conductor comprising armor Wires and aseparate layer of Wires terial of considerably greater conductivity thanthe armor Wires, said separate layer of Wires being spaced from eachother and from the armor Wires by material having insulating propertiessimilar to jute.

14. A cable in accordance with claim 13 in which the conductor isVprovidedwith plastic insulation and the armor Wires are spaced from theplastic insulation by material having insulating properties similar tojute.4

In Witness whereof, I hereunto subscribe my name this 26th day ofFebruary, A. D. 1926.

JOHN J. GILBERT.

